Jeff Layton [off-list ref] writes:

On Thu, 2023-08-10 at 00:17 +0900, OGAWA Hirofumi wrote:

quoted

Jan Kara [off-list ref] writes:

[...]

My mistake re: lazytime vs. relatime, but Jan is correct that this
shouldn't break anything there.

Actually breaks ("break" means not corrupt fs, means it breaks lazytime
optimization). It is just not always, but it should be always for some
userspaces.

The logic in the revised generic_update_time is different because FAT is
is a bit strange. fat_update_time does extra truncation on the timestamp
that it is handed beyond what timestamp_truncate() does.
fat_truncate_time is called in many different places too, so I don't
feel comfortable making big changes to how that works.

In the case of generic_update_time, it calls inode_update_timestamps
which returns a mask that shows which timestamps got updated. It then
marks the dirty_flags appropriately for what was actually changed.

generic_update_time is used across many filesystems so we need to ensure
that it's OK to use even when multigrain timestamps are enabled. Those
haven't been enabled in FAT though, so I didn't bother, and left it to
dirtying the inode in the same way it was before, even though it now
fetches its own timestamps from the clock. Given the way that the mtime
and ctime are smooshed together in FAT, that seemed reasonable.

Is there a particular case or flag combination you're concerned about
here?

Yes. Because FAT has strange timestamps that different granularity on
disk . This is why generic time truncation doesn't work for FAT.

Well anyway, my concern is the only following part. In
generic_update_time(), S_[CM]TIME are not the cause of I_DIRTY_SYNC if
lazytime mode.

-	if ((flags & S_VERSION) && inode_maybe_inc_iversion(inode, false))
+	if ((flags & (S_VERSION|S_CTIME|S_MTIME)) && inode_maybe_inc_iversion(inode, false))
		dirty_flags |= I_DIRTY_SYNC;

If reverted this part to check only S_VERSION, I'm fine.

Thanks.
-- 
OGAWA Hirofumi [off-list ref]